Influence of transdermal estradiol in the regulation of leptin levels of postmenopausal women: a double-blind, placebo-controlled study

Objective: To investigate whether the administration of transdermal estradiol is capable of modifying circulating levels of leptin. Design: Forty postmenopausal women randomly received in a double-blind fashion, a transdermal patch containing either placebo or estradiol (50 mug/day). After 2 months of treatment, they were switched to the alternate treatment for another 2 months. Leptin levels were measured at the end of the placebo and estradiol administration. In a subset of 28 women an evaluation of body composition via bioelectrical impedance and an oral glucose tolerance test (OGTT; 75 g) were also performed at the end of the placebo and estradiol administration. Glucose, insulin, and leptin levels were measured in all OGTT samples. Results: Leptin levels were related directly to body mass index (BMI), fat mass, and insulin, and inversely related to lean mass. In comparison to placebo, transdermal estradiol increased estradiol (from 77.8 +/- 8.4 pmol/l to 183.1 +/- 20.9 pmol/l; p < 0.0001) but did not significantly modify leptin (19.1 +/- 2.4 mug/l vs. 18.6 +/- 2 mug/l) or BMI. Estradiol did not modify fat mass or lean mass, significantly increased intracellular water (31.1 +/- 0.7% vs. 37.2 +/- 2.3%, p < 0.05), and decreased extracellular water (40.5 +/- 0.7% vs. 36.3 +/- 1.7%; p < 0.04). Leptin did not increase during OGTT, but a significant decrease, linearly related to BMI (r = 0.519; p = 0.0189), was observed at the end of the test. Conclusions: Low doses of transdermal estradiol exert no influence on fasting leptin levels or BMI. The possibility that different doses of estradiol exert a more pronounced effect on circulating leptin needs to be addressed in comparative studies.